BACKGROUND:Both self-regulation and insistence on sameness (IS) are related to anxiety, which is a common feature of individuals with autism spectrum disorder (ASD). Here, we aimed to characterise the IS-self-regulation-anxiety interrelationship by investigating the potential contribution made by self-regulation, assessed via effortful control (EC), to the IS-anxiety relationship in a sample of adolescents and young adults with ASD. METHOD:Seventy-one older adolescents and younger adults with ASD (49 males, 22 females; Mage = 18.71 years, SD = 2.51, range 14.42-24.81) completed the Adult Repetitive Behaviour Questionnaire-2, Effortful Control Scale of the Adult Temperament Questionnaire and the DSM-5 Dimensional Anxiety Scales. RESULTS:IS was associated with both EC (r = -.39, p = .001) and anxiety (r = .45, p < .001), and anxiety was in turn associated with EC (r = -.44, p < .001). To characterise the nature of this interrelationship, two mediation analyses were performed using the serial mediation model in PROCESS with 5000 resamples in bootstrapping. There was a significant indirect effect of EC on anxiety, through IS (b = -.06; BCa 95% CI [-.13, -.02]), and indirect effect on anxiety through EC (b = 1.62; BCa 95% CI [.59, 3.24]) with the mediators accounting for 29.07 and 26.04% of the total effect, respectively. CONCLUSIONS:Our study provides the first exploration of the IS-anxiety-self-regulation link in ASD. The finding that lower levels of self-regulation are related both to anxiety and IS behaviours points to self-regulation as a viable intervention target for both anxiety and IS behaviours.